Glossary - Part S

•  Screw-pile Towers: Lighthouses built on poles that were “screwed” into the sea floor. They often supported a small wooden building with a tower and light on top.

•  Secondary Lamp: A light source, which matched the main navigation light source’s intensity that was designed to replace the main source in the case of failure.

•  Sector: That part within the arc of a main navigation light exhibiting a different color by the use of a fixed colored filter to indicate a dangerous sea passage (red) or a fair way (white or green).

•  Sector Light: A lighthouse that indicates safe passage by a change in color when the mariner moves off course.

•  Sector Prism Panel: A panel of prisms external to the lens used to collect light and concentrate this light into a beam to mark a specific sector by diverting, intensifying, changing the color of the light or through combinations of these functions.

•  Service Rollers: Small wheels at the base of a fixed lens that allow convenient servicing.

•  Service Room: Where fuel and other supplies were kept.

•  Shoal: A shallow area, such as a sandbar or rock formation.

•  Shutter: Mechanically or electrically operated Venetian blinds that provide an occulting character.

•  Siren: A sound signal, which uses electricity or compressed air to actuate either a disc or a cup-shaped rotor.

•  Skeleton Tower: An open steel or aluminum tower not generally considered a heritage structure but may occupy the site of an historic Lighthouse.

•  Square Tapered: Four sided structure, almost exclusively made of wood in the Maritimes. Can be of dramatically varying heights.

•  Sodium Carbonate: Early glass produced was hygroscopic, meaning that it absorbed some of the sea air and water spray.

•  Sodium Seleniate Glass: Sodium Seleniate was added to glass to produce an orange-red color that could be used in the manufacture of glass filters to provide a red character or to mark a danger zone.

•  Sodium Silicate: Early glass produced was hygroscopic, meaning that it absorbed some of the sea air and water spray.

•  Solar-powered Optic: Many remote lights are powered today by batteries recharged by solar light.

•  Sound Signal: A device, which transmits sound, intended to provide information to mariners, during periods of restricted visibility and foul weather.

•  Spark Plug style light: A Caisson tower that looks somewhat like an automobile spark plug.

•  Spherical Aberration: A phenomenon of lens design that causes undesired deviations of the light from its perfect direction.

•  Spider Lamp: Shallow brass pan containing oil and several solid wicks.

•  Split Mirror: This design split the spherical-glass reflector, used at the back of some lenses, vertically into two half mirrors.

•  Stag Light: A lighthouse tended to only by men (i.e. no families).

•  Striae: An imperfection in the glass characterized by nearly transparent wavy lines or patches.

•  Subsidiary light: An additional light of lower intensity to the main navigation light, normally exhibited from a position below the main light to give warning of a nearby danger, such as a submerged reef, sand bank, shallow coastal water, etc.